Pressure vessels with bag filters are known. These vessels are for filtration of a liquid present in the system. All of these systems employ an external piping arrangement. In one example of a prior art, bag filter pressure vessel is a construction in which the inlet pipe must be detached in order to enter the pressure vessel. In this arrangement, a special elastomer seal is used in the form of a C which seals both the filter bag and the back-up restrainer basket's upper lip which must be inserted into the seal prior to the start up of the pressure vessel. Thereafter, as pressure is increased due to the filtration process the forces built up by the prevailing pressure enter the inner portions of the C seal to thereby expand the seal. The aforesaid construction and arrangement results in a positive force being applied to both the cover portion and the top of the vessel for a positive seal of the vessel to the atmosphere. Therefore, it must be apparent that the greater the internal pressure buildup within the pressure vessel the greater the sealing forces. However, the C-type seal is so constructed that with the greater pressure buildup, the C-type seal is expanded, and consequently the lesser the force applied on the ring portion of the filter bag which is located within the C-type seal. It should be evident, therefore, that the present arrangement always has the potential of bypassing the filter with undesirable dirt particles. Furthermore, it should be pointed out that once the filter bag is used or spent, the contaminated C-type seal, as well as the filter bag and the retainer basket, must all be physically handled and removed from the apparatus. In this particular arrangement, the unclean C-type seal must be stretched off the bag and the basket, and cleaned for reuse. Thereafter, the bag is disposed of and the retainer basket cleaned. Furthermore, all elements and members of this arrangement must be reassembled in order to render the pressure vessel ready for use again.
A second type of bag filter which is employed in a pressure vessel is provided with an elaborate hinge arrangement. In this construction a seal is inserted in a raised machined groove which is located laterally outside of the body of the vessel in order to provide a sealing area for the inlet piping. The pressure vessel is provided with a flat ring about the top of the body on the vessel and with a tab extension on the ring at the rear of the vessel.
In addition, a flat cover provided with an outer peripheral dimension, which is approximately the same as the flat ring, is affixed to the pressure vessel. The clamping action as a result of this securement squeezes the flat cover on the top and bottom side seals of the basket flange and on the inlet seal to create a sufficient pressure so that the system is hopefully adequately sealed. However, because of the construction and arrangement of the bag filter construction, it is difficult to get a positive, effective sealing of the vessel.
Another proposed arrangement for a pressure vessel bag filter relates to a construction in which the inlet feed is located below the level of the top of the filter bag and therefore a narrow, deep cavity is formed which receives the incoming liquid. The liquid spills over into the filter bag. Furthermore, a bevelled seat for the retainer basket is used, however if only a slight amount of differential downward force is applied to a part of the bag's ring, the bag may be shifted and unseated. Because of the difficulty in achieving a positive seal in this particular construction, a situation may arise in which bypassing of the filter bag results. When this happens, the contamination bypasses the filter and enters the downstream side of the pressure vessel thereby rendering the filtering media of the vessel much less effective.
Furthermore, the inlet cavity, as stated hereinbefore, is rather deep and narrow and cannot be effectively cleaned. Therefore, the hazard of recontamination of the pressure vessel is potentially present. This is especially true if the residue is not compatible with the next recycling of the filter.
Another filter construction that has been used in the past is an arrangement in which an inlet in the side wall of the pressure vessel is above the mouth opening of the filter bag. This arrangement can result in poor filtration since one of the principal features of the filter bag filtration is to not contaminate the downstream side of the filter, even after the filter has been spent or used. Thus, the retrieval of the spent filter bag permits the residual contaminant to spill over into the downstream side of the vessel thereby causing an unnecessary cleanup of the pressure vessel.
However, in spite of the drawbacks associated with the well-known pressure vessels having bag filters as set forth above, there are many obvious advantages of the filter bag concept of filtration over other methods of filtering. These advantages include: containing the contaminate in the filter bag for rapid disposal; a minimum of filtering liquid retained in the spent filter medium; a minimum cleanup of the vessel; prevention of contaminant downstream during the changeover or removal of the filter media; and minimizing the downtime necessary for changeover to insert the second filter. Moreover, in spite of the sealing problems in the inlet piping of the bag filters, as well as the problems in connection with sealing the filter bag against bypassing which are present in the above known constructions, the present invention overcomes these disadvantages and presents a novel and unique bag filter for a pressure vessel which operates efficiently and reliably.